Water culture or hydroponics is a cultivation method whereby plants are supported in a non-nutrient inert medium composed of quartz sand or the like, cultivation being carried out using a nutrient solution.
A water culture apparatus used for water culture principally comprises: plant containers which support plants during a period between germination and harvesting, and rafts which support a plurality of the plant containers and which are floated on the nutrient solution in order to supply nutrients to the plants.
Water-absorbent material having many lacunae, such as polyurethane foam or rock wool, is used in chips (which serve as the plant containers) in order to supply the plants with sufficient nutrients. Further, as shown in FIG. 30, chips 81 are mutually connected and are used as a unit body in order to reduce manual labor during plant management, sowing etc.
As shown in FIG. 36, a raft 84 is formed of material, such as expanded polystyrene, having a specific gravity lower than the specific gravity of water. The raft 84 has a plurality of vertically oriented channels 86 which support the chips 81. The vertically oriented channels 86 are formed in the raft 84 so as to be completely open from an upper surface to a lower surface of the raft 84. This arrangement permits a lower section of each of the chips 81 to come in contact with a nutrient solution 83 when the chips 81 are inserted into the vertically oriented channels 86. Accordingly, a sufficient amount of the nutrient solution 83 is supplied to the plants.
As shown in FIG. 30, when water culture is carried out, each of the mutually connected chips 81 is soaked sufficiently with the nutrient solution 83. Then, one seed 82 each of the plant is sown into each of the chips 81 and germinated, as shown in FIG. 31. Following this, as shown in FIG. 32, each of the connected chips 81 is separated and particularly well developed seedlings are selected from among those seedlings whose roots are well spread out. As shown in FIG. 33, the selected seedlings are then transplanted into the raft 84 which is floating on the nutrient solution 83. The seedlings are then allowed to grow on the raft 84 until they can be shipped as merchandise.
Plants grown by the method described above are conventionally shipped using the following handling method.
As shown in FIG. 34, the plants along with the chips 81 are taken out from the raft 84. Then, the plants along with the chips 81 are made into several bundles, packed into bags 85 as shown in FIG. 35, and shipped.
However, the conventional water culture method and plant handling method presents a problem in that a great deal of time and effort are required in carrying out the operations.
That is to say, in the conventional water culture method, the cultivator must transplant the chips 81, which support the plants, into the raft 84 when the plants have attained a certain stage of growth. Moreover, in this water culture method, before transplantation is carried out it is necessary to remove each of the chips 81 individually, and during transplantation care must be taken to prevent damage to the roots of the plants. Furthermore, when the grown plants are to be harvested, the cultivator must move around a water culture tank (not shown) which has the raft 84 floating therein, in order to pluck the plants. For these reasons the conventional water culture method presents the problem of requiring a great deal of time and effort for transplantation and harvesting operations.
Moreover, as shown in FIG. 35, in the conventional handling method it is necessary to make the harvested plants along with the chips 81 into several bundles in order to pack them for shipping. In this case, a great deal of labor is required to make the plants into bundles since the plants have been grown singly in each of the individually separated chips 81.
Further, as shown in FIG. 36, as the plants grow, the weight of the raft 84 increases and the raft 84 becomes partly submerged in the nutrient solution 83. Consequently, contact between each of the chips 81 and the nutrient solution 83 increases and excess water collects in the chips 81. This presents a problem in that root bases, the roots and other parts of the plants become over-humid or suffer from oxygen starvation.
In order to improve the growth environment of the plants, a 1979 Japanese Patent Application No. 7693 Laid-Open Publication (Tokukaisho 54-7693) discloses, as shown in FIG. 37, a raft 94 having air chambers 95 provided between channel wall sections 92 of vertically oriented channels 96 and groove sections 93, the groove sections 93 being provided along a rim of the raft 94. Since the buoyancy of the raft 94 increases due to the air chambers 95, even when the weight of the plants increases the raft 94 does not get submerged as much into a nutrient solution 83 as it otherwise would. Accordingly, excess water content in plant containers 91 which are inserted into the vertically oriented channels 96 also decreases.
However, excess water supply in the plant containers 91 also occurs due to a direct water supply resulting from the plant containers 91 being in contact with the nutrient solution 83. In the case of the raft 94 as well, this problem has not yet been resolved and, consequently, it is difficult to satisfactorily prevent excess water content from developing in the plant containers 91 and the problem of the root bases, the roots and other parts of the plants becoming over-humid or suffering from oxygen starvation remains.